The following two methods are generally known as intraocular pressure measuring methods. To be specific, there are employed a method of applying a predetermined pressure to a cornea to measure an intraocular pressure based on a depression state of the cornea, which is caused by the pressure and a method of estimating an intraocular pressure by bringing a presser into contact with the cornea (i.e., contact type) or by blowing compressed air to the cornea, based on an area ratio of the cornea deformed by the air pressure.
However, in those methods, the cornea is directly stimulated, so a high level of safety is required. In addition, a person to be examined has to bear a large burden such as a necessity of local anesthesia or discomfort feeling caused by air blowing.
Therefore, in order to solve such the problems, various methods have been proposed. That is, examples of the proposals include a method of vibrating a surface of an eyeball by a sound wave and measuring an intraocular pressure based on an amplitude of the vibration, a resonance frequency of the eyeball, or a velocity of a surface wave of the eyeball (see JP 02-180241 A, U.S. Pat. No. 5,375,595, and U.S. Pat. No. 5,251,627) and a method of pressing an eyeball in a closed-eye state through the eyelid to measure an intraocular pressure (see JP 06-105811 A, JP 08-280630 A, and JP 08-322803 A).